This study aims at examining in detail the linguistic characteristics of sentential idioms (‘idiomatische Sätze’, IS) in German, e.g. Das kannst du dir an den Hut stecken.; Du hast wohl Tomaten auf den Augen!; Da lachen ja die Hühner!. In theoretically and empirically investigating their syntactic, semantic and pragmatic features and productive potential, it is shown that IS can only be described properly by looking at the interfaces between syntax, semantics, and pragmatics, and by systematically investigating pattern formation. In this respect, the study goes far beyond traditional phraseological research. As a theoretical background, the study refers to research on phraseology, sentence types and sentence mood, linguistic evaluation, morphological productivity, and the frameworks of Construction Grammar and Relevance Theory. Empirical evidence comes from a large corpus of written German, a linguistic experiment on productivity, and introspective data. With respect to syntax, the study shows that IS are bound to one or a few different sentence types, varying according to the degree of restriction of their speech act potential. The complex semantics of IS is shown to consist not only of a literal and an idiomatic, but also of a third, mediating representational level. The idiomatic meaning of IS is described as evaluative meaning. Pragmatically, IS are dependent on special contextual environments to obtain a proper interpretation. A context model is developed which makes use of certain categories of evaluation. Moreover, a relevance-theoretic approach is sketched in order to explain which functional advantages IS might have compared to non-idiomatic utterances. With respect to productivity, ten different idiomatic patterns of construction are identified and described in detail. It is experimentally demonstrated that these patterns are productive to a greater or lesser degree dependent on their internal syntactic, lexical, semantic and pragmatic features.